bfd: Improve state change log message.

A log message like this one:

2024-01-09T06:45:17.201Z|00071|bfd(handler2)|INFO|ovn-0af536-0: BFD state
change: down->up "Neighbor Signaled Session Down"->"Neighbor Signaled Session
Down".

can be hard to read since '->' usually represents a status change, but
in this case the diagnostic code stays constant. Update the log message to
avoid such ambiguity. The log message for the above event become:

2024-01-09T06:45:16.211Z|00026|bfd(handler3)|INFO|ovn-0af536-0: BFD state
change: (bfd.SessionState: down, bfd.LocalDiag: "Neighbor Signaled Session
Down") -> (bfd.SessionState: up, bfd.LocalDiag: "Neighbor Signaled Session
Down")

Reported-by: Alex Stupnikov <astupnik@redhat.com>
Reported-at: https://bugzilla.redhat.com/2258496
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: Timothy Redaelli <tredaelli@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

lib/bfd.c

@@ -1130,10 +1130,11 @@ bfd_set_state(struct bfd *bfd, enum state state, enum diag diag)
         if (!VLOG_DROP_INFO(&rl)) {
             struct ds ds = DS_EMPTY_INITIALIZER;
 
-            ds_put_format(&ds, "%s: BFD state change: %s->%s"
-                          " \"%s\"->\"%s\".\n",
+            ds_put_format(&ds, "%s: BFD state change: (bfd.SessionState: %s,"
+                          " bfd.LocalDiag: \"%s\") -> (bfd.SessionState: %s,"
+                          " bfd.LocalDiag: \"%s\")\n",
                           bfd->name, bfd_state_str(bfd->state),
-                          bfd_state_str(state), bfd_diag_str(bfd->diag),
+                          bfd_diag_str(bfd->diag), bfd_state_str(state),
                           bfd_diag_str(diag));
             bfd_put_details(&ds, bfd);
             VLOG_INFO("%s", ds_cstr(&ds));